During the Northern Hemisphere winter, the subtropical jet stream stretches from the northern Africa, the Persian Gulf and Red Sea regions to the Himalayas. Numerical experiments with theoretical models have given some indication that the stationary wave amplitudes in both troposphere and stratosphere are sensitive to perturbations in the subtropical jet. A large and rapid increase in stratospheric wave amplitude is a recognized precursor to "sudden warming"; during a "sudden warming", the temperature at 10 mb near the north pole can increase by 40-60 degrees in a week, and the mean zonal wind can reverse from a westerly to an easterly direction. Unfortunately the routine upper air observations of this subtropical jet are extremely sparse. The meteorological information recorded on commercial flights can be of potential use. However, this information generally does not reach any of the major weather prediction centers worldwide. Under this award, Professor Tenenbaum will work with the British Airways to collect the meteorological recordings from certain flight paths in the region of the subtropical jet. Professor Tenenbaum will then analyze this data, evaluate the performance of weather prediction models in this data sparse region, and, if warrented, conduct data assimilation experiments. //
